Open Circuit Voltage Measurements Research Articles

Analysis of one-sun monocrystalline rear-contacted silicon solar cells with efficiencies of 22.1%

21.4% efficient rear-contacted cells (RCC) with interdigitated contact grids processed at the Fraunhofer ISE on 1.25 Ω cm float-zone (FZ) silicon are analyzed in detail. The comprehensive description does not only include a two-dimensional numerical device simulation, but also a detailed analysis of the optical carrier generation using optical ray tracing and determination of the losses due to distributed metal resistance and perimeter currents employing circuit simulation. Bulk and surface recombination losses are separated, combining carrier lifetime and open-circuit voltage measurements with numerical device simulation. The interface surface recombination velocity of the thermally oxidized emitter covering the front surface is deduced to be 1500 cm/s and the bulk diffusion length within the 1.25 Ω cm FZ silicon base is 1200 μm. Despite this excellent bulk diffusion length, the simulations reveal that at a maximum power point 80% of the total recombination is due to Shockley–Read–Hall recombination in the base. It was determined that losses due to the distributed metal resistance within the contact grid (including nongeneration losses) caused an fill factor decrease of 1% absolute. Loss currents flowing out of the cell perimeter caused an additional fill factor loss of 1.5% absolute. It was predicted that changing the surface concentration of the front and rear emitter diffusion from 5×1018 to 1×1018 cm−3, while keeping the sheet resistance constant, effected a relative improvement of 3% in the efficiency of the RCC structure. In fact, this modification has lead to an increase in the realized cell efficiency from 21.4% to 22.1% (VOC=697.6 mV, JSC=39.8 mA/cm2, and FF=79.4%), i.e., a relative improvement of 3.3%. This cell has an efficiency of 18.6% (VOC=696.5 mV, JSC=33.9 mA/cm2, and FF=78.8%) if illuminated from the rear side.

Determination of the Sodium Ion Transference Number of the Dion−Jacobson-Type Layered Perovskite NaCa2Nb3O10 Using ac Impedance and dc Methods

The electronic conductivity of the Dion−Jacobson-type layered perovskite NaCa2Nb3O10 was determined by employing ac impedance measurements using ion-blocking electrodes, electron-blocking electrodes, and dc Hebb−Wagner polarization measurements using NaCoO2 as the reversible reference electrode. Oxygen partial-pressure-dependent electrical conductivity studies revealed that the conductivity is nearly independent of the oxygen partial pressure in the range from 0.21 to 10-6 atm. Open-circuit voltage measurements of a galvanic cell employing air and 2 ppm of O2 in argon as electrodes revealed that layered perovskites appear not to be oxide ion conductors. The transference number for Na+ ions in NaCa2Nb3O10 at 550 °C is found to be 0.95 at the sodium activity of NaCoO2. The ac measurements using Na-β-alumina with electron-blocking electrodes and Pt-nonblocking electrodes produced similar impedance data at 550 °C suggesting a high ionic nature, which is consistent with the polarization study. However, the ionic and electronic conductivities varied depending on the experimental conditions, such as temperature and partial pressures.

Estimation of the membrane methanol diffusion coefficient from open circuit voltage measurements in a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) are attractive for several applications, however, at present, methanol crossover from the anode to the cathode appears to be a major limitation. For this reason, as one of the alternatives, membrane technology tries to obtain new methanol-impermeable polymer electrolytes. In this sense, it would be interesting to develop easy methods to check the new materials in relation to the methanol transport. In this work, a simple model is presented which permits to estimate easily the methanol diffusion coefficient of the membrane of a DMFC from open circuit voltage (OCV) measurements. The model has been checked in a DMFC using Nafion membranes as electrolyte.

Generalized analysis of quasi-steady-state and transient decay open circuit voltage measurements

The current–voltage characteristics of solar cells and photodiodes can be determined by measuring the open-circuit voltage as a function of a slowly varying light intensity. This article presents a detailed theoretical analysis and interpretation of such quasi-steady-state Voc measurements (QssVoc). The ability of this analysis to accurately obtain the true steady-state device characteristics even in the case of high lifetime, high resistivity silicon devices is demonstrated experimentally. The QssVoc technique can be used to determine the minority carrier lifetime, and the new generalized analysis is required to do this accurately. An important outcome is that solar cell and diode device characteristics can be obtained from measurements of either the photoconductance or the open-circuit voltage, even using transient techniques.

Synthesis and Electrical Properties of K- and Pr-Substituted LaGaO3 and LaInO3 Perovskites

Replacement of divalent ions by monovalent ions in decreases the electrical conductivity of LSGM and increases the activation energy to 1.42 eV. Substitution of La by substantial amounts of up to 50 atom % of Pr in LSGM yields new mixed oxide ion and electronic conductors. Substitution of 50 atom % Pr for La in the In-analog of LSGM, does not increase the electrical conductivity. Among the investigated oxides, exhibits the lowest activation energy of 0.44 eV and the highest electrical conductivity of at 200°C. Oxygen partial pressure dependence of the electrical conductivity reveals that LSIM and Pr-substituted LSIM perovskites are mixed oxide ion and p-type electronic conductors at high oxygen partial pressures. The electronic conductivity increases with increasing Pr content in LSIM. Open-circuit voltage measurements employing as separator in the galvanic cell show that the average transference number for oxide ion conduction is 0.78-0.90 in the temperature range 450-650°C. Powder X-ray diffraction data reveal that LSIM and Pr-substituted LSIM perovskites are not stable at low oxygen partial pressures of about while Pr-substituted LSGM retains the cubic perovskite structure. Accordingly, the new materials reported here may find application as electrode materials for solid oxide fuel cells and oxygen sensors. © 2001 The Electrochemical Society. All rights reserved.

Spatial effects on ideality factor of amorphous silicon pin diodes

We analyze dark current-voltage and short-circuit current versus open-circuit voltage measurements of hydrogenated amorphous silicon pin and nip diodes. The ideality factor of ∼1.4 is independent of the thickness of the intrinsic layer, indicating that recombination occurs in the p/i interface region rather than in the bulk. These results can be simulated accurately when the defect-pool model is used. Lateral amorphous silicon diodes with a uniform defect density throughout the intrinsic region have ideality factors, which do depend on the size of the intrinsic region and exceed the theoretical value of 2. We present a model to explain the ideality factor and to verify the results with numerical simulations. Values smaller than 2 are caused by unequal shifts of the quasi-Fermi levels for electrons and holes; values larger than 2 arise when the recombination is spread out over a wide region. In that case the distance between the quasi-Fermi levels is smaller than the applied voltage.

Boron-doped diamond-like amorphous carbon as photovoltaic films in solar cell

In this paper, the photovoltaic feature of metal-boron carbide-silicon (MCS) solar cell was reported. The boron-doped diamond-like carbon thin film on n-silicon substrate has been prepared using arc-discharge plasma chemical vapor deposition (PCVD) technique. The conductivity and the resistivity of the film were measured by Bio-Rad Hall5500PC system to be p-type semiconductor and 3–12 Ω cm/□, respectively. The boron content in the films was about 0.8–1.2%, obtained from Auger electron spectroscopy (AES), and some microcrystalline diamond grains (0.5–1.0 μm) embedded in the mainly amorphous network were revealed through scanning electron microscope (SEM) and Raman spectrum. The performance of Au/C(B)/n-Si heterojunction solar cells has been given under dark I– V rectifying curve and I– V working curve (with 100 mW cm −2 illumination). A measurement of open-circuit voltage V oc=580 mV and short-circuit current density J sc=32.5 mA cm −2 was obtained. Accordingly, the energy conversion efficiency of the device was tentatively determined to be about 7.9% in AM 1.5, 100 mW/cm 2 illuminated.

Lithium nickel oxyfluoride (Li 1− zNi 1+ zF yO 2− y) and lithium magnesium nickel oxide (Li 1− z(Mg xNi 1− x) 1+ zO 2) cathodes for lithium rechargeable batteries : II. Electrochemical investigations

Two series of Mg substituted and F substituted nickelates were prepared, among them Li 1− z Ni 1+ z F y O 2− y ( y=0.015, z=0.06) and Li 1− z (Mg x Ni 1− x ) 1+ z O 2 ( x=0.05, z=0.08) have shown improved cycling performance compared to un-substituted LiNiO 2. Cyclic voltametry (CV), quasi open circuit voltage (QOCV) measurements, and X-ray diffraction all indicate that phase transitions in the charge and discharge reactions are partially suppressed after F or Mg substitution. Excessive substitution, however, results in reduced capacity and the lack of electrochemical activity. For Li 1− z Ni 1+ z F y O 2− y this is explained by the increasing presence of divalent nickel ions at the lithium 3b sites. For Li 1− z (Mg x Ni 1− x ) 1+ z O 2, the presence of Mg ions at the lithium sites is more likely the reason.

Improvement of failure detection of production line test results by implementing Δ V criteria

The reliability of automotive batteries is an important factor, especially for the OEM market. To ensure consistent reliability all automotive batteries are subjected to electrical load tests prior to shipment. These tests are performed in accordance with industry accepted standards. It is essential that the energy discharged from the battery during test be minimized to avoid the cost and delay associated with recharge. When defining the ideal high rate discharge test process one must consider these basic requirements. Immediately after formation, and preferably, after post cleaning, batteries are discharged at high current for a few seconds. The voltage under load at the end of test is determined and compared to nominal values resulting in a pass/fail decision. This paper discusses the effectiveness of the present high rate discharge test evaluation criteria in terms of it’s ability to accurately discriminate between acceptable and unacceptable batteries. Variations in materials and manufacturing processes affect open-circuit voltage (OCV) and constant current voltage (CCV) measurements leading to erroneous pass/fail determinations. The paper will illustrate how these variations can be recognized and statistically evaluated. A supplemental evaluation criterion is presented which significantly improves the reliability of test results. This criterion is the gradient Δ V of the discharge curve. Evaluation of test data using this criterion yields information that directly correlates to the failure mode of the rejected battery, including irregularities in pasting and assembly. This paper concludes that the implementation of Δ V criterion significantly improves the failure detection of batteries subjected to production line high-rate discharge tests. Using the Δ V criterion to evaluate the test results is a more accurate determinant of an acceptable battery than the traditional criteria and results in fewer customer returns.

Photogalvanic effect in aqueous Methylene blue nickel mesh systems: Conversion of light into electricity

The photogalvanic effect in electrochemical cells, employing aqueous Methylene blue and Fe(II)/Fe(III) couple electrolyte and nickel-mesh electrodes, were experimentally investigated. Five different standard H-cell configurations were set-up by modifying the electrolyte. Long-term open-circuit voltage measurements were conducted in order to test the stability of the cells. Light on–off reproducibility experiments were also carried out during lengthy cell operations. By comparing experimental quantum yield with theoretical predictions, it was found that the cells operate on differential electrode kinetics. Oxidation of the illuminated electrode was detected. This affected the current–voltage characteristics of the cells after a sufficiently long cell operation. Schottky junction treatment was used to model the electrolyte–electrode junction. After calculating the ratio between the majority carrier (electron) current density and minority carrier (hole) current density, we concluded that the oxidation of the electrodes contributes positively to the cell performance since the electrode–electrolyte interface shows unipolar Schottky diode characteristics. Copyright © 2001 John Wiley & Sons, Ltd.

AA′2M3O10 (A = K, Rb, Cs; A′ = Ca; M = Nb) layered perovskites: low-temperature proton conductors in hydrogen atmospheres

Electrical conductivity of the Dion–Jacobson (D–J) type layered perovskite oxides, AA′2M3O10 (A = K, Rb, Cs; A′ = Ca; M = Nb, Ta), is determined by AC impedance analysis in hydrogen atmospheres and in air. The electrical conductivity behavior of the layered perovskite oxides in hydrogen is different from that in air. Among the layered perovskites, KCa2Nb3O10 exhibits the highest electrical conductivity, σ, of 3.2 × 10−4 S cm−1 at 45 °C with an activation energy, Ea, of 0.25 eV in a hydrogen atmosphere. Open circuit voltage measurements at room temperature with hydrogen–oxygen gas concentration cells reveal that the mobile charge carriers are most likely protonic in origin. The electrical (proton) conductivity is comparable to that of fast lithium ionic conductors based on the perovskite structure such as (Li,La)TiO3 at the same temperature.

Potentiometric measurements of the spin-split subbands in a two-dimensional electron gas

The density of states of carriers in a high-mobility InAs single quantum well is spin split by the Rashba effect. The asymmetry favors down-spin states for carriers with positive momentum and up-spin states for carriers with negative momentum. Imposing a bias current causes inequivalent shifts of the spin subband chemical potential, which are detected using a ferromagnetic film electrode and an open circuit voltage measurement. Measurements made on three samples over a range $77<T<296\mathrm{K}$ demonstrate spin detection at a ferromagnet-semiconductor interface and corroborate earlier experimental results of spin-dependent interfacial resistance.

Molybdenum chemistry in molten LiCl–KCl eutectic: an electrochemical and absorption spectroscopy study of the concentration dependent stability of solutions of K 3MoCl 6

The chemical behaviour of LiCl–KCl–K 3MoCl 6 solutions between 400 and 500°C was investigated. They underwent slow decomposition, according to a concentration dependent disproportionation reaction yielding metallic molybdenum and a volatile black higher valency molybdenum compound, which corresponded with MoCl 5. Chronopotentiometric determinations showed a single 3-electron reduction, yielding Mo. The process was slow with diffusion-controlled mass transfer. The concentration of the Mo(III) species, presumed in the form of MoCl 6 3− ions, was determined using linear sweep voltametry and open circuit voltage measurements and the overall Mo(III) species concentration by chemical analysis. The results showed MoCl 6 3− to be the predominant species in the melt and the presence of a previously proposed dinuclear species, Mo 2Cl 9 3−, could not be confirmed electrochemically. This arose to quantification errors in the determination of the electroactive species MoCl 6 3− due to inherent problems in estimating the active surface area of the electrode. The electronic absorption spectrum of MoCl 6 3− in LiCl–KCl eutectic at 400°C is reported for the first time. Measurements were made above and below 0.045 mol dm −3 K 3MoCl 6, the concentration above which the disproportionation reaction was relatively slow. The results are discussed in detail and the spectroscopic parameters of the octahedral MoCl 6 3− complex were calculated as: Dq=1775 cm −1, B=511 cm −1 and C=1913 cm −1. Although an additional band, at 340 nm, appeared during disproportionation it could not be identified with any currently known polynuclear molybdenum chloro complex or oxychloro complex. It is probably associated with an intermediate in the disproportionation process. No spectral evidence was thus obtained in support of the formation of dinuclear molybdenum species.

Characterisation of composite SOFC cathodes using electrochemical impedance spectroscopy

Porous composite cathodes for solid oxide fuel cells (SOFCs) made from a mixture of lanthanum strontium manganite (LSM) and yttria stabilised zirconia (YSZ) are investigated using electrochemical impedance spectroscopy (EIS) at temperatures between 850° and 1000°C. The aim of the investigations is to determine the total polarisation resistance and to identify the mechanism of the oxygen reduction process. A minimum of two overlapping arcs can be distinguished in the impedance spectra. It is, however, difficult to correlate these arcs to specific elementary processes in the oxygen reduction process, as the measured impedance is very sensitive to test circumstances. The standard resistor settings (i.e., current measurement range) on the measurement equipment has been found to affect the measured impedance. Furthermore, the electrode performance is influenced by the previous electrochemical history of the specific electrode. Finally, the reproducibility of electrode characterisation as evaluated from obtained impedance spectra is examined. The consequence of these problems is discussed. Two cell geometries are compared: a symmetrical two electrode geometry suitable for open circuit voltage measurements with good reproducibility and a three-electrode geometry for polarised measurement with a less convincing reproducibility.

Chromium Chevrel phase sulfide (Cr xMo 6S 8− y) as the cathode with long cycle life in lithium rechargeable batteries

Chromium Chevrel phase sulfide (CrCPS: Cr x Mo 6S 8− y ) was investigated as the cathode in lithium rechargeable batteries. This compound had a triclinic unit cell in a wide range of chromium composition. Electrochemical cells based on the intercalation of lithium into both stoichiometric and nonstoichiometric CrCPS were examined by a long-term cycling in deep discharge depth at a relatively high constant current density. The nonstoichiometric Cr 1.3Mo 6S 7.7 showed a long cycle life more than 1000 cycles in the voltage range from 2.7 V to 1.5 V except for the first cycle and an energy density of at least 140 Wh kg −1 of active material. Almost no change of crystal structure before and after 1000 cycles contributed to such an excellent cycle performance. From the open circuit voltage (OCV) measurement and X-ray diffraction analysis we propose the reaction models and also estimate the lithium intercalation sites for triclinic CrCPS.

Hysteresis observed in quasi open-circuit voltage measurements of lithium insertion in hydrogen-containing carbons

High capacities with large hysteresis were observed during lithium insertion in hydrogen-containing carbons heated at temperatures near 700 °C. Quasi open-circuit voltage (OCV) measurements were used to study these materials. Using a simple model developed previously [1], we can qualitatively model the result of the OCV measurement. It is believed that the lithium atoms bind near aromatic hydrogen at edge of each graphene layer in the materials. This activated process involves a carbon-carbon bonding change from (sp) 2 to (sp) 3 leading to large hysteresis during lithium insertion.

Hydroxyl ion conduction in ytterbium-doped strontium cerate at T<580 K in H2O/air atmosphere

Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.

The chemostat: A novel approach to the synthesis of manganese dioxide

The development and use of the chemostat, an apparatus which controls pH, Eh and temperature during redox reactions, is described. Its application is illustrated for the synthesis of the birnessite variety of manganese dioxide, via 2(x − 1)MnO 4 − + (7 − 2x)Mn 2+ + (8 − 3x)H 2O ↔ 5MnO x + 2(8 − 3x)H + where x is the oxygen index of the manganese dioxide. The chemostat controls the pH and Eh of the precipitation reaction by the judicious addition of KOH and KMnO 4 solutions, respectively, as well as maintaining a constant temperature in the precipitation cell. Using the control conditions outlined herein, the average errors associated with the pH, Eh and temperature were ±0.2 pH units, ±0.025 V and ±0.5 °C, respectively. The birnessite samples that were produced were characterized in terms of X-ray diffraction, x in MnO x and open circuit voltage measurements. These properties were found to have a strong dependence on the synthetic conditions.

Preparation and properties of CdS/CdTe thin film solar cell produced by periodic pulse electrodeposition technique

CdS/CdTe solar cells have been prepared by periodic pulse electrodepositionmethod. 10.8% efficient cell was made with open circuit voltage (Voc)≈753mV, short-circuit current (Jsc)≈23.6 mA/cm2 and fill factor (FF)≈0.61. Current-voltage-temperature measurments showed the variation of ideality factor (A) from 1.88 at 344 K to 4.49 at 202 K whereas voltage factor (α) was almost constant above 276 K. The junction transport is possibly dominated by a tunneling mechanism. Capacitance measurements gave the value of diffusion potential as 1.2 eV, ionized charged density as 5.9 × 1015 cm-3 and number of interface states (NIS) as 2.8 × 1011 cm-2 eV-1 at zero volt bias. Measurements of open circuit voltage (Voc) with temperature gave the value of barrier height as 1.42 eV.

Preparation and properties of electrodeposited indium tin oxide/SnO2/CdTe and indium tin oxide/SnO2/CdS/CdTe solar cells

Cadmium telluride-based solar cells have been prepared as indium tin oxide (ITO)/SnO2/CdTe and indium tin oxide/SnO2/CdS/CdTe structures where CdS and CdTe were prepared by an electrodeposition technique. Both open circuit voltage and short circuit current of ITO/SnO2/CdTe cells were higher than that of ITO/SnO2/CdS/CdTe cells. The spectral response measurement showed that the current collection was higher in the ITO/SnO2/CdTe cell relative to the ITO/SnO2/CdS/CdTe cell. Current-voltage temperature measurements indicated that the junction transport could be controlled by recombination or thermally assisted tunneling in the ITO/SnO2/CdTe cell, whereas tunneling could be the dominant junction transport mechanism in the ITO/SnO2/CdS/CdTe cell. Activation energies of ITO/SnO2/CdTe and ITO/SnO2/CdS/CdTe cells were 0.60 and 0.76 eV, respectively. The values of the built-in potential, Vbi calculated from the measurement of open circuit voltage with temperature were 1.41 and 1.5 eV for ITO/SnO2/CdTe and ITO/SnO2/CdS/CdTe cells, respectively, whereas from Mott–Schottky plots they were 1.1 and 0.95 eV, respectively.